Method and apparatus for attaching solder members to a substrate

ABSTRACT

The invention discloses a method for attaching solder members ( 114 ) to a substrate ( 112 ). The method includes forming a decal ( 110 ) with a plurality of solder members ( 114 ). The method further comprises aligning the decal ( 110 ) with the substrate ( 112 ) and transferring the solder members ( 114 ) on the decal ( 110 ) to the substrate ( 112 ).

TECHNICAL FIELD OF THE INVENTION

[0001] This invention relates generally to the field of electronicdevices packaging and more particularly to a method and apparatus forattaching solder members to a substrate.

BACKGROUND OF THE INVENTION

[0002] Modern electronic components utilize numerous integratedcircuits. Often, these integrated circuits must be electricallyconnected to each other or to other electronic components. One methodfor connecting integrated circuits to electronic components utilizes anarea array electronic package. Some examples of area array electronicpackage designs are a ball grid array electronic package and a flip-chipelectronic package. With a ball grid array electronic package, variousinput and output ports of an integrated circuit are typically connectedvia wire bonds to contact pads on the ball grid array electronicpackage. Solder balls formed on the contact pads of the ball grid arrayelectronic package are used to complete the connection to anotherelectronic component, such as a printed circuit board. Integratedcircuits are also connected to electronic components through a flip-chipelectronic package design. The flip-chip electronic package is similarto the ball grid array electronic package in that solder balls are usedto make a connection with other electronic components, such as a printedcircuit board. However, solder balls in a flip-chip design are attacheddirectly to the input and output ports on the face of the integratedcircuit. Flip-chip packages do not require wire bonds. One importantstep in the above described methods for interconnecting electroniccomponents is the formation of solder balls on the ball grid arraypackage or flip-chip electronic package.

[0003] Several conventional methods exist for attaching solder balls toa ball grid array or flip-chip electronic packages. Flip-chip solderbumps may be fabricated on the integrated circuit by evaporation orplating while the solder necessary for a ball grid array electronicpackage may be achieved by solder paste printing or vacuum loadingpreformed solder balls onto a substrate through the use of a vacuumchuck. The use of a vacuum chuck to transfer preformed solder balls tothe contact pads on the ball grid array package suffers severaldisadvantages. For example, the minimum distance between solder ballsthat this method allows may be unacceptable in some applications.Additionally, this conventional method may require two vacuum chucksbecause while one vacuum chuck is transferring solder balls to the ballgrid array electronic package, the other is being filled. The use of oneor more vacuum chucks increases the expense associated with this methodfor forming solder balls on an electronic package. Furthermore, if asolder ball is not transferred properly, any adjustment, such as addinga missing solder ball, must be made by hand.

[0004] Another conventional method for attaching solder to a ball gridarray or flip-chip electronic package utilizes a stencil placed on topof the package. In a typical application, solder paste is applied on topof the stencil and then a squeegee is moved across the top of thestencil forcing the solder paste down through the holes until contact ismade with the contact pads of the ball grid array or flip-chipelectronic package. This method also suffers several disadvantages. Forexample, the stencil requires cleaning. Additionally, the stencils tendto deteriorate because the solder paste may wear on the stencils.Furthermore, the use of solder paste may be more expensive than the useof solder balls.

SUMMARY OF THE INVENTION

[0005] Therefore, a need has arisen for a new method and apparatus thatovercomes the disadvantages and deficiencies of the prior art. Theinvention comprises a method and apparatus for attaching solder membersto a substrate.

[0006] According to one aspect of the invention, the method comprisesthe step of forming a decal. The decal comprises a plurality of soldermembers. The method further comprises aligning the decal with asubstrate and transferring the solder members on the decal to thesubstrate.

[0007] According to another aspect of the invention, a method forforming a decal for transferring solder member to a substrate comprisesthe step of forming a plurality of apertures in a substrate and placinga plurality of solder members on the substrate. The method furthercomprises allowing the plurality of solder members on the substrate toenter the plurality of apertures to form a decal having a plurality ofsolder members.

[0008] The invention provides a method for attaching solder members to asubstrate that facilitates precise alignment of the solder members withdesired locations on the substrate. Because only the decal requiresalignment, in contrast to aligning multiple solder members with desiredlocations on a ball grid array package, precise alignment of all soldermembers with desired locations on the ball grid array package may bemade through one alignment process. Missing balls are often a problem inconventional ball grid array production lines. The invention may enhancethe production efficiency and yield of non-missing balls by screeningout defective decals before shipment to a vendor. This screening processcontrasts with conventional screening that may take place afterattachment of solder balls to the ball grid array package.

[0009] The invention also allows for the formation at a central site ofsolder member decals that may be shipped to remote locations fortransferring the solder members to the ball grid array package.Therefore, much of the equipment conventionally used to place solder ona ball grid array can be eliminated, which may reduce the cost offorming solder balls on ball grid arrays. Any equipment required toproduce the solder member decal may reside solely at a centralizedlocation. Formation of a solder member decal also facilitates delegationto third parties of a portion of the solder ball attachment process,which may further reduce costs. Because the solder member decals may beformed without solder paste, the use of solder member decals does notexpose the ball grid array package or other substrate to which soldermembers may be attached to the harshness of such a chemical process. Theuse of preformed solder members eliminates the expense of usingenvironmentally unfriendly chemicals. The use of solder balls ratherthan solder paste also provides a more uniform distribution of solderand allows the use of various types of solder alloys.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] For a more complete understanding of the present invention andthe advantages thereof, reference is now made to the followingdescriptions taken in connection with the accompanying drawings inwhich:

[0011]FIGS. 1A through 1C are simplified side view illustrations ofmethod steps according to the teachings of the present invention;

[0012]FIG. 2A is a top view of an exemplary integrated circuit packageutilizing the invention;

[0013]FIGS. 2B AND 2C are side views of the integrated circuit packageshown in FIG. 2A;

[0014]FIG. 2D is a top view of a flip-chip electronic package design inwhich an integrated circuit has solder balls attached to its contactpads;

[0015]FIG. 2E is a side view of the flip-chip electronic package shownin FIG. 2D;

[0016]FIG. 3A is a top view of an exemplary solder member decalaccording to the invention;

[0017]FIG. 3B is a side view of the solder member decal shown in FIG.3A.

[0018]FIG. 4 is a top view of an exemplary ball grid array package;

[0019]FIG. 5 is a flow chart illustrating one method of attaching solderballs to an electronic package according to the invention;

[0020]FIG. 6 is a side view of one embodiment of the solder member decalshown in FIG. 1A and a side view of the ball grid array package shown inFIG. 1A;

[0021]FIG. 7 is a side view of the solder member decal and ball gridarray package shown in FIG. 6 and illustrates the transfer of solderballs from the solder member decal to a ball grid array package;

[0022]FIG. 8 is a flow chart illustrating one method of attaching solderballs to a ball grid array package utilizing the solder member decalshown in FIGS. 6 and 7;

[0023]FIG. 9 is a side view of another embodiment of the solder memberdecal shown in FIG. 1A;

[0024]FIG. 10 is a side view of the solder member decal shown in FIG. 9and the ball grid array package shown in FIG. 1A and illustrates thetransfer of solder balls from the solder member decal to the ball gridarray package;

[0025]FIG. 11 is a flow chart illustrating one method of attachingsolder balls to a ball grid array package utilizing the solder memberdecal shown in FIGS. 9 and 10;

[0026]FIG. 12 is a side view of another embodiment of the solder memberdecal shown in FIG. 1A;

[0027]FIG. 13 is a side view of the solder member decal shown in FIG. 12and the ball grid array package shown in FIG. 1A and further illustratesthe transfer of solder balls from the solder member decal to the ballgrid array package;

[0028]FIG. 14 is a flow chart illustrating one method of attachingsolder balls to a ball grid array package utilizing the solder memberdecal shown in FIG. 12;

[0029]FIG. 15 is a side view of another embodiment of the solder memberdecal shown in FIG. 1A and a photomask used in the formation of thesolder member decal;

[0030]FIG. 16 is a side view of the solder member decal shown in FIG. 15and the ball grid array package shown in FIG. 1A and further illustratesthe transfer of solder balls from the solder member decal to the ballgrid array package; and

[0031]FIG. 17 is a flow chart illustrating one method of attachingsolder balls to a ball grid array package utilizing the solder memberdecal shown in FIGS. 15 and 16.

DETAILED DESCRIPTION OF THE INVENTION

[0032] The invention and its advantages are best understood by referringto FIGS. 1 through 17 of the drawings, like numerals being used for likeand corresponding parts of the various drawings.

[0033]FIGS. 1A through 1C illustrate an embodiment of the invention. InFIG. 1A a ball grid array (BGA) package 112 is illustrated. In oneembodiment, the invention provides a method for attaching soldermembers, such as solder balls 114, to a substrate, such as ball gridarray package 112. Elements commonly used in solder alloys are tin,lead, silver, bismuth, copper, indium, antimony, and cadmium; however,any suitable elements for use as solder may be used to form soldermembers, such as solder balls 114. Ball grid array package 112 may be aconventional ball grid array package. Examples of conventional ball gridarray substrate materials include organic laminates, ceramics, metalsand polymeric sheets and films. Ball grid array package 112 may alsocomprise any suitable substrate to which solder members may be attachedto facilitate electrical connection of electronic devices. Also, asdiscussed in greater detail below, solder members may be attacheddirectly to other substrates, such as, for example, an interposer or anintegrated circuit in a flip-chip electronic package. FIG. 1A alsoillustrates one embodiment of a solder member decal 110 according to theinvention. Solder member decal 110 comprises a substrate 111 with aplurality of solder members, such as solder balls 114, formed thereon.Solder balls 114 may alternatively be replaced with solder membershaving a variety of configurations, such as solder columns, which arecylindrical in shape. According to the invention, solder balls 114 aretemporarily formed or placed on substrate 111 for subsequent transfer toball grid array package 112. As discussed in greater detail below, ballgrid array package 112 may comprise a plurality of contact pads (notshown explicitly in FIGS. 1A through 1C). According to one embodiment ofthe invention, solder balls 114 may be transferred to the contact padson ball grid array package 112.

[0034]FIG. 1B illustrates the step of aligning solder member decal 110with ball grid array package 112. According to the invention, solderballs 114 may be attached to ball grid array package 112 at desiredlocations by alignment of solder member decal 110 with ball grid arraypackage 112, bringing solder balls 114 into contact with a portion ofball grid array package 112, and subsequent transfer of solder balls 114to ball grid array package 112. As discussed in greater detail below,solder member decal 110 may be placed on top of ball grid array package112 to facilitate transfer of solder balls 114 from solder member decal110 to ball grid array package 114. Alternatively, ball grid arraypackage 112 may be placed on top of solder member decal 110. Inaddition, other suitable orientations of solder member decal 110 andball grid array package 112 that facilitate transfer of solder balls 114to a ball grid array package 112 may be utilized. After aligning soldermember decal 110 with ball grid array package 112, solder balls 114 maybe transferred to ball grid array package 112. This transfer process mayinclude a solder reflow process. Solder member decal 110 may be removedfrom solder balls 114 to produce an attachment-ready ball grid arraypackage 116, shown in FIG. 1C. Solder member decal 110 may be removedfrom the ball grid array package 112 at various points in theabove-described process. For example, solder member decal 110 may beremoved from solder balls 114 and ball grid array package 112 before orafter a solder reflow process.

[0035]FIG. 1C illustrates an attachment-ready ball grid array package116. Solder balls 114 are securely attached to ball grid array package112 to form attachment-ready ball grid array package 116. Solder balls114 formed on attachment-ready ball grid array package 116 may provide aplurality of electrical connection points to facilitate connection ofone electronic device to another. The solder balls 114 on the attachmentready ball grid array package 116 may be attached to contact pads ofvarious electronic components, such as a printed circuit board.

[0036]FIGS. 2A, 2B, and 2C illustrate one example of a integratedcircuit package 210 utilizing an attachment-ready ball grid arraypackage 116 according to the invention. Integrated circuit package 210comprises an attachment-ready ball grid array package 116 with anintegrated circuit 214 formed thereon. Integrated circuit 214 may beattached to attachment-ready ball grid array package 116 with an epoxy224, as shown in FIG. 2B. Various integrated circuit connection ports220 are electrically connected via wire bonds 216 to bond pads 230 onattachments ready ball grid array package 116. As shown in FIG. 2A, bondpads 230 are electrically connected to contact pads 412 by electricallyconductive interconnect lines 240. Contact pads 412 are shown best inFIG. 4. The interconnect lines 240 may be patterned in one or morelayers, with some of the interconnect lines 240 placed below the surfaceof the attachment-ready ball grid array package 116. Solder balls 114are connected to contact pads 412. Wire bonds 216 may be free-standingwires. As illustrated in FIG. 2C, integrated circuit connection ports220 are electrically connected to contact pads 226 on a printed circuitboard 222 by connecting printed circuit board contact pads 226 to solderballs 114. To environmentally protect the integrated circuit 214 fromthe potentially corrosive nature of the atmosphere, the regionsurrounding the integrated circuit 114, bond wires 216, and bond pads230, may be filled with polymeric material 250. Therefore, the formationof solder balls 114 on contact pads 412 facilitates connection ofprinted circuit board contact pads 226 to ball grid array contact pads412, which allows electrical connection between integrated circuit 214and printed circuit board 222. Thus, the invention provides a method forforming solder balls 114 on a ball grid array 112 that facilitates theconnection of an integrated circuit, such as integrated circuit 214, toanother electronic component, such as printed circuit board 222.

[0037]FIGS. 2D and 2E illustrate an example of a flip-chip electronicpackage 260 and its connection to a printed circuit board 282. Flip-chip260 is another example of a substrate onto which solder members may beformed according to the invention. As illustrated in FIGS. 2D and 2E,flip-chip electronic package 260 allows connection of the integratedcircuit 264 to printed circuit board 282 without the use of wire bondssuch as wire bonds 216 and without use of bond pads such as bond pads230. Solder balls 114 are formed directly on various connection ports280, which may be formed flush with a surface of integrated circuit 264.Integrated circuit 264 is substantially similar to integrated circuit214. Solder balls 114 electrically connect the integrated circuitconnection ports 280 to contact pads 286 on printed circuit board 282,as shown in FIG. 2E. After connection, a polymeric or elastomericunderfill material 290 is applied between the integrated circuit 264 andthe printed circuit board 282 to protect the integrated circuit 264 fromthe environment and to provide strain relief to the electronic package.

[0038]FIGS. 3A and 3B further illustrate details of an exemplary ofsolder member decal 110. The solder member decal 110 shown in FIGS. 3Aand 3B comprises a plurality of solder balls 114 formed around theperimeter of solder member decal 110 to match the pattern of contactpads 412 formed on ball grid array package 112 shown in FIG. 4.According to the invention, a pattern of solder members, such as solderballs 114 may be formed on a solder member decal, such as solder memberdecal 110, to match a corresponding pattern of contact pads on asubstrate, such as ball grid array package 112;

[0039]FIG. 4 illustrates an example of ball grid array package 112. Ballgrid array package 112 is formed with an integrated circuit receivingarea 410 for placement of an integrated circuit. Ball grid array package112 is further formed with a plurality of ball grid array contact pads412 to facilitate connection of the integrated circuit to anotherelectronic device. Contact pads 412 may be formed flush with the surfaceof ball grid array package 112.

[0040]FIG. 5 is a flow chart illustrating one method of attaching solderballs 114 to a ball grid array package 112. With reference to FIGS. 1through 5 and particularly FIG. 5, the operation of one embodiment ofthe invention is described. The method begins at step 510. According tothe invention, at step 520 a solder member decal 110 is formed with aplurality of solder balls 114 arranged in a pattern to match acorresponding pattern of contact pads 412 on a ball grid array package112. As discussed in greater detail below, a variety of techniques maybe used to form solder balls 114 on a preformed solder connection decal110. Such techniques may comprise, for example, forming a plurality ofbosses in a substrate and allowing solder balls 114 to fall into thebosses through gravity, forming holes in a substrate and allowing thesolder balls to fall into the holes through the application of negativepressure, further applying an adhesive film to the substrate having aplurality of holes, and forming a film with a pattern of adhesiveregions. These exemplary techniques are discussed in greater detailbelow.

[0041] At step 530, solder member decal 110 is aligned with a ball gridarray package 112 so that solder balls 114 are in contact with contactpads 412. Because solder member decal 110 is formed with a pattern ofsolder balls 114 that matches a pattern of contact pads 412 on ball gridarray package 112, all of solder balls 114 may be aligned withrespective contact pads 412 with one alignment step.

[0042] At step 540, solder balls 114 are transferred to contact pads 412of ball grid array 112. According to one embodiment of the invention,solder balls 114 are transferred to contact pads 412 through a solderreflow process. The solder reflow process securely attaches solder balls114 to contact pads 412 of ball grid array package 112. Solder reflowprocesses are well known and a variety of types of solder reflowprocesses may be used to secure solder balls 114 to contact pads 412.Solder reflow processes may be performed in a nonoxidizing atmosphere,such as nitrogen; however, an oxygen atmosphere such as air may also beappropriate.

[0043] Solder flux may be placed on either contact pads 412 or solderballs 114 before bringing the two into contact with each other andheating both the solder member decal 110 and ball grid array package112. Alternatively, solder member decal 110 is removed from ball gridarray package 112 before heating the ball grid array package 112 leavingsolder balls 114 on ball grid array package 112. Various other processesmay be incorporated with the invention that are operable to securelyattach solder balls 114 to contact pads 412, including fluxless solderreflow processes. Substrate 111 may comprise a variety of materials.Although a variety of materials may be used, it is desirable that thesubstrate 111 comprise materials that can withstand the heat incurredduring the transfer process and to which solder will not stick. Forexample, suitable materials include plastic, aluminum, silicon, quartz,or ceramics. Alternatively, materials that will burn off during atransfer process, such as paper, may be used.

[0044] The type of solder that may be used in a solder reflow processmay be determined by the material used to form the ball grid arraypackage 112. In addition, the type of material that may be used forsubstrate 111 of solder member decal 110 may be affected by the type ofsolder reflow process selected. For example, high lead solders areconventionally chosen for ceramic packages. If a ball grid array package112 comprises a ceramic package, high lead solders may be selected.Because high lead solder may require maximum temperatures of 350° C. ormore, the material used for substrate 111 may be chosen to withstandthat temperature, or alternatively selected so that it will burn offduring the solder reflow process.

[0045] The reflow process securely attaches solder balls 114 to contactpads 412. At step 550, substrate 111 is peeled from the ball grid arraypackage 112 leaving an attachment ready ball grid array package 116.Alternatively, the material of substrate 111 may be chosen to burn offduring the reflow process. Thus, the invention provides a method thatfacilitates the attachment of solder balls to a substrate, which in turnallows the connection of various electronic devices. The methodillustrated in FIG. 5 ends at step 560. The method illustrated in FIG. 5may be used to form solder members on a plurality of substrates inaddition to the ball grid array package 112, such as flip-chipelectronic package 260 or an interposer (not explicitly shown).

[0046]FIGS. 6 through 8 illustrate another method for attaching solderballs 114 to a ball grid array package 112 according to the inventions.As discussed in conjunction with FIGS. 1 through 5, solder balls 114 maybe replaced with solder members having a variety of configurations.FIGS. 6 and 7 are side views of solder member decal 610 and ball gridarray package 112. FIG. 8 is a flow chart illustrating steps associatedwith the attachment of solder balls 114 to ball grid array package 112through the use of solder member decal 610. Solder member decal 610comprises a substrate 611 formed with a plurality of indentations orbosses 612. In one embodiment, solder member decal 610 is formed from anon-solderable material, or in other words, a material that is notwetted by solder, such as aluminum. Bosses 612 may comprise a variety ofconfigurations. For example, bosses 612 may be formed with aconfiguration of a frustum, as shown in FIG. 6, or other suitableconfigurations that are operable to retain a solder ball. Bosses 612should be formed with a depth sufficient to retain solder balls 114. Forexample, in one embodiment, bosses 612 are formed with a depth ofapproximately eighty percent the diameter of solder balls 114. Theformation of bosses 612 is illustrated at step 820 in the flow chartshown in FIG. 8.

[0047] At step 830, solder balls 114 may be placed in bosses 612 byplacing a plurality of solder balls on the surface of solder memberdecal 610 and allowing the solder balls 114 to fall into the bosses 612under the influence of gravity. At step 840, excess solder balls 114 maybe removed from solder member decal 610 through a variety of techniques,such as tilting or vibrating the solder member decal 610.

[0048] At step 850, solder member decal 610 is aligned with ball gridarray package 112. After solder balls 114 are placed within bosses 612,the ball grid array package 112 is aligned with the solder member decal610 and solder balls 114 are brought into contact with ball grid arraycontact pads 412. To facilitate transfer of solder balls 114 to contactpads 412, flux may be placed on contact pads 412. Placing flux oncontact pads 412 also removes any oxide that may have formed on thecontact pads. Flux may also be placed on solder balls 114. Becausesolder balls 114 remain in bosses 612 due to the influence of gravity,the ball grid array package 112 is placed on top of the solder memberdecal 110 to align the two, as shown in FIG. 6. If desired, however,forces other than gravitational forces, such as electrostatic forces,may be applied to solder balls 114 to maintain solder balls 114 inbosses 612 in an upside-down configuration. After alignment of the ballgrid array package 112 with the solder member decal 610, the solderballs 114 may be secured to the ball grid array contact pads 412. Oneexample of a process for securing solder balls 114 to the ball gridarray contact pads 412 is a solder reflow process, such as the solderreflow process discussed in conjunction with FIG. 5.

[0049] The step 850 of aligning solder member decal 610 with ball gridarray package 112 may comprise the step 854 of inverting the soldermember decal 610 after alignment to facilitate removal of substrate 611,as shown in FIG. 7. Inversion also reduces the weight that may beapplied to the solder balls 114 by the ball grid array package 112, thusreducing the likelihood that solder balls 114 will become deformed.Deformed solder balls may, however, be rounded by performing a secondsolder reflow. At step 860, after inversion, substrate 611 may beremoved, leaving solder balls 114 in contact with the ball grid arraycontact pads 412. The flux placed on contact pads 412 providessufficient adhesion to help hold the solder ball 114 on contact pads412. At step 870, solder balls 114 may then be secured to contact pads412 through a solder reflow process. Removal of substrate 111 reducesthe overall weight of the solder member decal 610 and ball grid arraypackage 112 combination. Therefore, removal of substrate 111 may reducethe time required for the solder reflow process due to the reducedweight. The method according the embodiment of the invention shown inFIGS. 6 through 8 ends at step 880. The method illustrated in FIGS. 6through 8 may be used to form a plurality of solder members, such assolder balls 114, on a plurality of substrates in addition to the ballgrid array package 112, such as flip-chip electronic package 260 or aninterposer.

[0050] In addition to the advantages previously discussed with using asolder member decal to form solder members on a substrate, theembodiment shown in FIGS. 6 through 8 also provides the additionaladvantage that it is a non-vacuum process. Thus, a vacuum tool is notrequired with this embodiment of the invention, which may further reducethe costs associated with forming solder members on a substrate tofacilitate connection of electronic components. According to theabove-described procedure, a plurality of preformed solder connectionsmay be attached to a ball grid array or other similar substrate tofacilitate electrical connection of electronic devices.

[0051]FIGS. 9 through 11 illustrate another method for attaching soldermembers to a substrate according to the invention. FIGS. 9 and 10 areside view illustrations of solder member decal 910 and ball grid arraypackage 112. FIG. 11 is a flow chart illustrating steps associated withthe attachment of solder balls 114 to ball grid array package 112through the use of solder member decal 910. Solder member decal 910comprises a thin substrate 911 formed with a plurality of apertures 912and a bottom surface 913. Substrate 911 is formed from a material thatis not wetted by solder, such as aluminum, and is approximately 0.0030inches thick. However, other materials and substrate thicknesses may beused. Apertures 912 are formed with a size and configuration operable tofirmly hold solder balls 114. In one embodiment, the solder balls 114extend below the bottom surface 913 sufficiently to make contact withthe contact pads 412 of the ball grid array package 112. The formationof apertures 912 in substrate 911 is illustrated at step 1120 in FIG.11. At step 1130 a plurality of solder balls 114 are placed on substrate911. At step 1140, in order to place solder balls 114 in apertures 912,negative pressure, such as a vacuum 914, is applied to the lower surfaceof the substrate 911, as shown in FIG. 9, to pull solder balls 114 intoapertures 912. At step 1145, excess solder balls 114 may be removed fromsolder member decal 910 through a variety of techniques, such as tiltingor blowing them off with air. At step 1150, in order to facilitatetransportation of solder member decal 910, an additional thin cover 1012may be formed to top of solder balls 114 and substrate 911 to holdsolder balls 114 in place, as shown in FIG. 10. In one embodiment, cover1012 is formed from aluminum and is approximately 0.0010 to 0.0020inches thick. However, other thicknesses and materials for cover 1012may be used.

[0052] After solder balls 114 are placed in apertures 912, the soldermember decal 910 is aligned with the ball grid array package 112 at step1160 with the bottom side 913 of the solder member decal 910 facing thecontact pads 412, as shown in FIG. 10. To facilitate a solder reflowprocess, flux may be formed on ball grid array contact pads 412. Througha solder reflow process, such as the one described above in conjunctionwith FIG. 5, solder balls 114 may be secured to contact pads 412. Step1170 in FIG. 11 illustrates the solder reflow process. When solder balls114 are heated during the solder reflow process, the solder balls 114melt and are secured to ball grid array contact pads 412. In step 1180,the solder member decal 910 and thin cover 1012 are removed from thesolder balls 114 following the solder reflow process, leaving the solderballs 114 attached to the ball grid array package 112. The methoddescribed in conjunction with FIGS. 9 through 11 produces anattachment-ready ball grid array package 116 as shown in FIG. 1C. Themethod of the embodiment of the invention illustrated in FIGS. 9 through11 ends at step 1190. The method illustrated in FIGS. 9 through 11 maybe used to form a plurality of solder members, such as solder balls 114,on a plurality of substrates in addition to the ball grid array package112, such as flip-chip electronic package 260 or an interposer.According to the above-described procedure, a plurality of soldermembers, such as solder balls 114, may be attached to a ball grid arrayor other similar substrate to facilitate electrical connection ofelectronic devices. In addition to the advantages of solder memberdecals previously discussed, the embodiment discussed in conjunctionwith FIGS. 9 through 11 is particularly advantageous because of its easeof use and the low operating cost associated with the use of materialssuch as aluminum for the decal substrate 911.

[0053]FIGS. 12 through 14 illustrate another method for attaching soldermembers, such as solder balls 114, to a substrate according to theinvention. FIGS. 12 and 13 are side views of solder member decal 1210and ball grid array package 112. FIG. 14 is a flow chart illustratingsteps associated with the attachment of solder members, such as solderballs 114, to a substrate, such as a ball grid array package 112,through the use of a solder member decal 1210. Solder member decal 1210is substantially similar to solder member decal 910 except that soldermember decal 1210 is formed with an adhesive film 1214 attached to thebottom surface of substrate 1211. The adhesive film 1214 may be appliedto the bottom surface of substrate 1211 in several ways. For example,the adhesive film 1214 may be applied onto a second substrate such as aplastic sheet or film (not shown). This plastic sheet may then beapplied to the bottom surface of substrate 1211. Alternatively, theadhesive film 1214 may be applied directly to the bottom surface ofsubstrate 1211. Substrate 1211 may comprise a variety of materials,including aluminum. Solder member decal 1210 is also formed with aplurality of apertures 1212. The formation of apertures 1212 and theprovision of adhesive film 1214 is illustrated in FIG. 14 at steps 1420and 1430, respectively. At step 1440, solder balls 114 are placed withinapertures 1212 in the same manner as that discussed in conjunction withFIGS. 6 through 8. The adhesive film 1214 helps secure the solder balls114 within apertures 1212. Once solder balls 114 are placed withinapertures 1212, the solder member decal 1210 may be inverted and alignedat step 1445 with ball grid array package 112 as shown in FIG. 13.Excess solder balls 114 may then be removed as discussed above inconjunction with FIGS. 6 through 8. The adhesive film 1214 possessessufficient adhesive properties such that solder balls 114 will adhere tothe adhesive film 1214 when solder member decal 1210 is inverted. Theadhesive film 1214 should not, however, leave any residue on the solderballs 114. At step 1450, the combination of the solder member decal 1210and the ball grid array package 112 may be heated to transfer the solderballs 114 to the ball grid array contact pads 412 through a solderreflow process. During the reflow process, the adhesive film is burnedoff. After transfer of the solder balls 114, the substrate 1211 may bepeeled off of attachment-ready ball grid array package 116. The methodof the embodiment of the invention illustrated in FIGS. 12 through 14ends at step 1460.

[0054] Adhesive film 1214 may comprise an ultraviolet sensitive tapesuch as that described in U.S. Pat. No. 5,356,751, entitled Method andProduct for Particle Mounting, issued to Cairncross et al. on Oct. 18,1994, which loses its adhesive properties when exposed to ultravioletlight. U.S. Pat. No. 5,356,751 is incorporated herein by reference forall purposes. If ultraviolet sensitive tape is used, the adhesive film1214 may be exposed through the top of adhesive film 1214 afteralignment of the solder member decal 1210 and the ball grid arraypackage 112. Therefore, the substrate 1211 and the adhesive film 1214may be removed from the ball grid array package 112 before the reflowprocess, leaving the solder balls 114 on the ball grid array package112. Removal of the substrate 1211 and the adhesive film 1214 before thereflow process may reduce the time required by the solder reflowprocess. Thus, according to the above-described procedure, a pluralityof solder members, such as solder balls 114 may be attached to a ballgrid array or other substrate to facilitate electrical connection ofelectronic devices.

[0055]FIGS. 15 through 17 illustrate another method for attaching soldermembers to a substrate 112. FIGS. 15 and 16 are side views of soldermember decal 1510 and ball grid array package 112. FIG. 17 is a flowchart illustrating steps associated with the attachment of soldermembers, such as solder balls 114, to a substrate, such as ball gridarray package 112, through the use of solder member decal 1510. Soldermember decal 1510 comprises an adhesive film 1512. Adhesive film 1512 isa light sensitive adhesive film that has a specially formulated adhesivesurface 1515 that loses much of its adhesive properties when exposed toultraviolet light. Adhesive film 1512 also comprises a second surface1513. Adhesive film 1512 may comprise an adhesive film such as thatdescribed in U.S. Pat. 5,356,751, entitled Method and Product forParticle Mounting, issued to Cairncross et al. on Oct. 18, 1994.Adhesive films suitable for use with the invention are also availablefrom manufacturers such as Ultron and Lintec.

[0056] As shown in FIGS. 15 and 17, at step 1720 a photomask 1514 isplaced over adhesive film 1512. Photomask 1514 is fabricated with aplurality of regions or dots 1520 in a configuration that matches theconfiguration of contact pads 412 on the ball grid array package 112. Atstep 1730, areas of the adhesive film 1512 that are not covered by thedots 1520 of photomask 1514 are exposed to ultraviolet light 1516. Areasof the adhesive film 1512 that are covered by the dots 1520 of photomask1514 are not exposed to the ultraviolet light 1516. Therefore, areas onthe adhesive film 1512 corresponding to areas on the photomask 1514 withdots 1520 possess their full adhesive properties while the remainder ofthe adhesive film 1512 loses much of its adhesiveness. At step 1740 thephotomask 1514 is removed. After removal of the photomask 1514 at step1750, the adhesive film 1512 may be flooded with solder balls 114. Thesolder balls 114 will adhere only to the areas of the adhesive film 1512corresponding to areas on the photomask 1514 with dots 1520. Any excesssolder balls 114 may be blown off adhesive film 1512 with air. Once theplurality of solder balls 114 are formed on adhesive film 1512, they maybe transferred to a ball grid array package 112.

[0057] After formation of solder balls 114 on adhesive film 1512, soldermember decal 1510 is inverted, as shown in FIG. 16, and aligned on topof ball grid array package 112 such that solder balls 114 are in contactwith ball grid array package contact pads 412. This step is illustratedat step 1760 in FIG. 17. Before applying a solder reflow process, atstep 1770 the adhesive film 1512 may be removed by exposing the adhesivefilm 1512 to ultraviolet light 1616 through the second surface 1513. Theultraviolet light 1616 acts through the second surface 1513 to cause theareas on the adhesive surface 1515 previously shielded by the photomaskto lose their adhesive properties. Application of ultraviolet light 1516to second surface 1513 after alignment of the solder member decal 1510and the ball grid array package 112 therefore releases solder balls 114from the adhesive film 1512 and allows the adhesive film 1512 to beremoved. After removing the adhesive film 1512, the solder balls 114 maybe secured to the ball grid array package 112 at step 1780 through, forexample, a solder reflow process such as the one described above. Themethod of the embodiment illustrated in FIGS. 15 through 17 ends at step1790.

[0058] The invention therefore provides a method for attaching soldermembers to a substrate that facilitates precise alignment of the soldermembers with desired locations on the substrate. Because only the decalrequires alignment, in contrast to, for example, aligning multiplesolder members with desired locations on the ball grid array package,precise alignment of all solder members with desired locations on theball grid array package may be made through one alignment process.Missing balls are often a problem in conventional ball grid arrayproduction lines. The invention may enhance the production efficiencyand yield of non-missing balls by screening out defective decals beforeshipment to a vendor. This screening process contrasts with conventionalscreening that may take place after attachment of solder balls to theball grid array package.

[0059] The invention also allows for the formation at a central site ofsolder member decals that may be shipped to remote locations fortransferring the solder balls on the ball grid array package. Therefore,much of the equipment conventionally used to place solder on a ball gridarray can be eliminated, which may reduce the cost of forming solderballs on ball grid arrays. Any equipment required to produce that soldermember decal may reside at a centralized location. Formation of a soldermember decals also facilitates delegation to third parties of a portionof the solder member attachment process, which may further reduce costs.Because solder member decals may be formed without solder paste, the useof solder member decals does not expose the ball grid array package tothe harshness of such a chemical process. The use of preformed soldermembers also eliminates the expense associated with usingenvironmentally unfriendly chemicals. The use of solder members such assolder balls rather than solder paste also provides a more uniformdistribution of solder and allows the use of various types of solderalloys.

[0060] Although the invention has been particularly shown and describedby the foregoing detailed description, it will be understood by thoseskilled in the art that various other changes in form and detail may bemade without departing from the spirit and scope of the invention.

What is claimed is:
 1. A method for attaching solder members to asubstrate comprising the steps of: forming a decal comprising aplurality of solder members; aligning the decal with a first substrate;and transferring the plurality of solder members on the decal to thefirst substrate.
 2. The method of claim 1 wherein the step of aligningthe decal with the first substrate further comprises bringing theplurality of solder members into contact with a portion of the firstsubstrate.
 3. The method of claim 1 wherein the step of transferring thesolder members comprises heating the solder members.
 4. The method ofclaim 1 wherein the step of transferring the solder balls comprises asolder reflow process.
 5. The method of claim 1 wherein the step offorming a decal comprises arranging the solder members in a patterncorresponding to a pattern of contact pads formed on the firstsubstrate.
 6. The method of claim 1 wherein the step of forming a decalfurther comprises forming a plurality of apertures in a secondsubstrate.
 7. The method of claim 6 wherein the step of forming a decalfurther comprises affixing an adhesive film to the second substrate. 8.The method of claim 1 wherein the step of forming a decal furthercomprises forming indentations in second substrate.
 9. The method ofclaim 1 wherein the step of forming a decal further comprises placing aplurality of solder members on a plurality of portions of an adhesivefilm.
 10. The method of claim 7 and further comprising applying a lightsource to the adhesive film.
 11. The method of claim 1 wherein the firstsubstrate comprises a flip-chip electronic package.
 12. The method ofclaim 1 wherein the first substrate comprises a ball grid array.
 13. Themethod of claim 1, wherein the plurality of solder members comprises aplurality of solder columns.
 14. The method of claim 1, wherein theplurality of solder members comprises a plurality of solder balls. 15.The method of claim 1, wherein the step of transferring a plurality ofsolder members comprises a plurality of solder reflow processes.
 16. Themethod of claim 4, wherein the solder reflow process is performed in anitrogen environment.
 17. A method for forming a decal for transferringsolder members to a substrate comprising the steps of: forming aplurality of apertures in a first substrate; placing a plurality ofsolder members on the first substrate; and allowing the plurality ofsolder members on the first substrate to enter the plurality ofapertures to form a decal having a plurality of solder members.
 18. Themethod of claim 17 wherein the step of allowing the plurality of soldermembers on the first substrate to enter the plurality of aperturescomprises applying a vacuum to the plurality of apertures.
 19. Themethod of claim 17 and further comprising applying an adhesive film tothe first substrate to secure the plurality of solder members in theplurality of apertures.
 20. The method of claim 17 wherein the firstsubstrate comprises aluminum.
 21. The method of claim 17 and furthercomprising placing a cover on top of the solder members to secure theplurality of solder members in the plurality of apertures.
 22. Themethod of claim 21 wherein the cover comprises a non-solderablematerial.
 23. The method of claim 21 wherein the cover comprisesaluminum.
 24. The method of claim 17 wherein the step of forming aplurality of apertures in a first substrate comprises forming aplurality of apertures in a pattern to match a pattern of contact padson a second substrate.
 25. The method of claim 24 wherein the secondsubstrate comprises a ball grid array.
 26. The method of claim 24wherein the second substrate comprises a flip-chip electronic package.27. The method of claim 17 wherein the plurality of solder memberscomprise a plurality of solder balls.
 28. The method of claim 19 whereinthe adhesive film is operable to lose its adhesive properties uponapplication of ultraviolet light.
 29. A method for forming a decal fortransferring solder members to substrate comprising the steps of:forming a plurality of indentations in a first substrate; placing aplurality of solder members on the first substrate; and allowing theplurality of solder members on the first substrate to enter theplurality of indentations to form a decal having a plurality of soldermembers.
 30. The method of claim 29 wherein the step of allowing theplurality of solder members on the first substrate to enter theplurality of indentations comprises allowing the plurality of soldermembers to fall into the plurality of apertures under the influence of agravitational field.
 31. The method of claim 29 wherein the firstsubstrate comprises a non-solderable material
 32. The method of claim 29wherein the first substrate comprises aluminum.
 33. The method of claim29 wherein the step of forming a plurality of indentations in a firstsubstrate comprises forming a plurality of indentations in a pattern tomatch a pattern of contact pads on a second substrate.
 34. The method ofclaim 29 wherein the indentations comprise a frustum.
 35. The method ofclaim 33 wherein the second substrate comprises a ball grid array. 36.The method of claim 33 wherein the second substrate comprises aflip-chip package.
 37. The method of claim 33 wherein the plurality ofsolder members comprises a plurality of solder balls.
 38. A method forattaching solder members to a substrate comprising the steps of: placinga photomask adjacent a film to expose a plurality of exposed areas andshield a plurality of shielded areas, the film being adhesive andfurther being operable to lose a portion of its adhesiveness whenexposed to ultraviolet light; applying ultraviolet light to the exposedareas of the film; placing a plurality of solder members on the film;allowing the plurality of solder members to adhere to the plurality ofshielded areas of the film; aligning the film with a first substrate;and transferring the solder members on the film to the first substrate.39. The method of claim 38 wherein the step of aligning the film withthe first substrate further comprises bringing the plurality of soldermembers into contact a portion of the first substrate.
 40. The method ofclaim 38 wherein the step of transferring the solder members comprisesheating the solder members.
 41. The method of claim 38 wherein the stepof transferring the solder members comprises a solder reflow process.42. The method of claim 38 and further comprising the step of formingthe photomask to have a pattern of photomask regions corresponding to apattern of contact pads on the first substrate.
 43. The method of claim38 wherein the adhesive film comprises a first surface and a secondsurface and the step of allowing the plurality of solder members toadhere to the plurality of shielded areas of the film comprises the stepof allowing the plurality of solder members to adhere to the firstsurface and further comprising the step of applying ultraviolet light tothe second surface to facilitate removal of the film from the soldermembers.
 44. The method of claim 43 wherein the step of transferring thesolder members comprises a solder reflow process and further comprisingremoving the film before the solder reflow process.
 45. The method ofclaim 38 wherein the step of aligning the film with a first substratecomprises aligning the film with a ball grid array.
 46. The method ofclaim 38 wherein the step of aligning the film with a first substratecomprises aligning the film with a flip-chip electronic package.
 47. Themethod of claim 38 wherein the step of placing a plurality of soldermembers on the film comprises placing a plurality of solder balls on thefilm.